RESUMO
The reaction of Morita-Baylis-Hillman ketones with 2-aminothiophenol mediated by Cs2CO3 results in an oxidative cyclization to 2,2-disubstituted dihydro-1,4-benzothiazines, with the structure of the product indicating the occurrence of an aza-Michael addition along the pathway. In contrast, in the absence of a base, the parent compounds interact to produce a thia-Michael adduct instead. A deeper mechanistic study improved our understanding of the apparent contradiction and provided insight into the base-dependent switch in reactivity.
RESUMO
A serendipitous Rauhut-Currier dimerization of 1,1-disubstituted activated olefins derived from Morita-Baylis-Hillman adducts was observed in the presence of DABCO. The reaction is driven by the migration of an acyl group and produces multifunctionalized enol esters in yields greater than 90% in most cases, without necessitating column chromatographic purification. The acyl transfer is thought to proceed via a transition state typical of a Morita-Baylis-Hillman (MBH) reaction, supported by a brief mechanistic study involving computational calculations.
RESUMO
An oxidative cyclization ensued upon interaction of Morita-Baylis-Hillman (MBH) ketones with 2-aminothiophenol in the presence of Cs2CO3, resulting in the formation of new 2,2-disubstituted dihydro-1,4-benzothiazines. The reaction features an aza-Michael addition and an oxidative cyclization involving the formation of a carbon-sulfur bond and works well over a wide range of MBH ketones to deliver the dihydrobenzothiazines in good yields in reasonable reaction times under mild conditions.
RESUMO
Owing to its exceptional properties at high temperature, graphite is used in several applications such as structural material and fuel block in high temperature nuclear reactors. Air ingress is one of the serious safety concerns in these reactors. Oxidation of graphite leading to increased porosity affects its mechanical strength and may lead to core collapse resulting in a severe accident. During such a scenario, generation of graphite particles could be the main hazard. Once generated, these particles often in fine and ultrafine sizes, may carry radioactivity to large distances and/or for long times. These particles owing to their higher surface to volume ratio possess an additional inhalation hazard. Ultrafine particles have the potential to enter into respiratory tract and cause damage to body organs. Coating of graphite components is preferred to reduce the oxidation induced damages at high temperatures. In the present work, effect of alumina (Al2O3) coating on the emission characteristics of particles from graphite under high temperature conditions has been investigated. Bare and Al2O3 coated graphite specimens were heated within a closed chamber at varying temperatures during these experiments. Temporal evolution of concentrations of gases (CO and CO2) and particles were measured. The results reveal that Al2O3 coating on the graphite delayed the oxidation behavior and the structure of graphite remained largely intact at high temperatures. A significant reduction in aerosol formation and CO emission was also noticed for the coated specimens.
RESUMO
A degradative dimerisation of Morita-Baylis-Hillman ketones was observed in the presence of a primary diamine. The reaction proceeded swiftly to produce methylene-bridged 1,3-dicarbonyl compounds. A brief mechanistic investigation alluded to a retro-Mannich reaction as the key step of the transformation.
RESUMO
A serendipitous carbon-carbon bond cleavage in the reaction of benzoyl acrylates, derived from Morita-Baylis-Hillman adducts, with hydrazines delivered new N',N'-disubstituted benzohydrazides. The reaction features a regioselective formation of two carbon-nitrogen bonds and works well with a range of acrylates and hydrazines. A brief mechanistic investigation alluded to a cyclic hemiaminal as a plausible intermediate.